Journal
GEOCHEMICAL JOURNAL
Volume 49, Issue 2, Pages 175-184Publisher
GEOCHEMICAL SOC JAPAN
DOI: 10.2343/geochemj.2.0343
Keywords
marine humic-like fluorescent dissolved organic matter; photobleaching; solar irradiation; size distribution; hydrophobic/hydrophilic properties
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Funding
- Ministry of Education, Culture, Sports, Science and Technology of Japan [14340166, 19310003]
- Grants-in-Aid for Scientific Research [14340166, 19310003] Funding Source: KAKEN
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We examined the molecular weight distribution of the fluorescence intensity of FDOMM and dissolved organic carbon (DOC) concentrations in the subtropical western North Pacific, in order to characterize photoreactivity of FDOMM and understand the relationship between FDOMM and DOC pool. DOC concentrations in a hydrophobic fraction (O-DOC), which is extracted by solid phase extraction, accounted for 34 and 38% of bulk organic carbon in the surface and deep layer. FDOMM in a hydrophobic fraction (O-FDOMM) acceunted for 78 and 37% of FDOMM in the surface and 1000-m depth seawater, respectively. Molecular weight distribution of O-FDOMM and 0-DOC showed that ratio of the fluorescence intensity to the DOC concentration of each MW fraction increased with depth. This suggests that the contribution of O-FDOMM to O-DOC in the deeper seawater is higher than that in the surface layer. When deep-seawater samples were irradiated by natural sunlight for 5 days, the fluorescence intensity of O-FDOMM decreased to almost half and its molecular weight shifted to lower one, whereas the O-DOC concentration did not decrease. It implies that a part of O-FDOMM remains as photobleached FDOMM (no-fluorescence DOM) after photobleaching.
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